For both commercial and test applications there is a need to be able to feed electric signals from a flat or ribbon cable through a connector to PCB circuitry. High quality signal transmission has been difficult to achieve because of stringent signal performance requirements coupled with the constraints of limited space requirements both in the connector and on the board.
Various designs of ribbon cable have been used, such as a row of insulated signal cable imbedded in a strip of insulation with a sheet of conductive shielding placed on one side of the strip of insulation or a sheet or strip of conductive shielding material placed on both sides of the insulation. Neither arrangement addresses the well-known problem of line-to-line cross-talk between the individual signal conductors within a cable.
It is also known to arrange alternating signal and ground conductors in the insulation of a cable with shielding on one or both sides of the strip of insulation bearing the signal and ground conductors. This arrangement of ground and signal conductors and their shielding is not adequate to control cross-talk among the various conductors. Impedance within the cable is also not controlled, except within broad limits, the range of impedance depending on the materials used in the cable and the spacing and dimensions of the various parts, for example. To achieve better signal transmission quality than available in the above cables, one has been required to resort to coaxial signal cables, wherein each signal conductor is individually shielded from outside electrical influences and any signals being transmitted within a conductor are shielded from leaking outside the cable as well. The space required for coaxial cables is greater than for unshielded signal transmitting conductors and terminating them to connectors properly requires much more complicated connectors which are usually larger, much more expensive to manufacture, and time consuming and expensive to execute the termination process thereon. Many of the resulting terminated coaxial cables are too bulky to fit into required small spaces on PCB's for connection.
Most of the problems cited above which pertain to the construction and properties of the ribbon cable itself may be solved by use of a shielded ribbon cable wherein each signal conductor is insulated by porous expanded polytetrafluoroethylene polymer, such as that described in U.S. Pat. Nos. 3,953,566, 3,962,153, 4,096,227, 4,187,390, 4,902,423, and 4,428,665. As a unit, the insulated signal conductors are shielded by a conductive metal shield on each side of the plane of the row of signal conductors and a protective layer of polymer jacketing placed, usually by extrusion, on the outside of the shielding. The jacketing, shielding, and insulation between each signal conductor is flattened or compressed to leave a narrow web of material between each signal conductor along its length, of about four mills thickness, for example. The inclusion of shielding in the webs and the virtual squeezing out of insulation between the layers of shielding of the webs essentially eliminates line-to-line cross-talk between the signal conductors of the ribbon cable to give a cable having near coaxial cable electrical and signal performance levels. IDC signal conductor contacts can be used to terminate the conductors of the cable while retaining near coaxial performance.
The present invention provides a connector which, when used to terminate the above cable, will overcome the problems outlined above without use of coaxial cable shielding.